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Let's say you want to visit cities A, B and C, which are set in a triangle, so you can choose to travel A-B-C-A or A-C-B-A. The roads from A to B and A to C are fine, but the one between B and C is a notoriously dangerous twisty mountain road where accidents happen all the time (think Yungas Road). All things being equal, is it safer to drive up or down the road?

If that's too hypothetical, the actual inspiration for this was this weekend's trip from Sydney to Wollongong and Canberra. The shortest route between the latter two is the Illawarra Highway across the Macquarie Pass (Google map), where recommended speeds at some bends dip to as low as 15 km/h. Especially in bad weather, when it's rainy, foggy and slippery, it seems that if you go up, you're likely to get flattened by a truck careening down around a hairpin curve, while if you go down, you're likely to lose control yourself...

Update: Anecdotes, logic and physics are all good, but the best answer would involve actual accident data!

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    I'm pretty sure you've just answered that in the question -- going up shifts the risk to the ability of other drivers, going down the question is more if you can drive. So, assuming you know how to drive down a slippery mountain slope (slowly, low gear, test your breaks first) then down is safer. If your driving isn't good then they're probably much the same (and you shouldn't be doing it).
    – SpaceDog
    Dec 23, 2015 at 4:22
  • Accident data would not be any better answer, as the majority of accidents are due to human error, weather, and such not the direction you are traveling. Just like no having any deaths does not make Qantas the "safest" airline, more like the luckiest.
    – user13044
    Dec 23, 2015 at 8:17
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    I think the relative risk depends on the road, traffic, and other conditions. If it's a relatively empty road (very low traffic), then going up is probably safer, as the only risk you're facing is your own inability to navigate the road. If there is heavy traffic, especially with large vehicles, in a region where safety practices are not well enforced, going uphill may be more dangerous, as the odds of being hit head-on by an out-of-control truck may be much higher than your odds of driving over the edge, etc. Whether it's a 2- or 4-lane road likely matters, too, etc...
    – Flimzy
    Dec 23, 2015 at 8:58
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    Drive A to B then B to A then A to C?
    – JonathanReez ♦
    Dec 23, 2015 at 9:32
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    If you're worried enough about the B-C road that you have to ask, then @JonathanReez's answer must be best :)
    – Julia Hayward
    Dec 23, 2015 at 15:21

7 Answers 7

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Down is more dangerous.

There are three factors contributing to this.

When you need to decide on a slowdown in case of potential accident, you basically need to annihilate momentum, and when you are going up, gravity contributes to the total work needed to slow down. When you are going down, gravity works against your intent to slow down, and brakes alone against gravity cant do the same job as brakes plus gravity in case of going up.

Second, brakes can ... well ... break. I know of a driver who actually burned his brakes while going down. It was a Russian military truck in Caucasus mountains with manual transmission and the driver was not that experienced with it.

Third, when you brake your vehicle's stability depends on the force on the brakes. When you brake hard as you go down, you can send the vehicle to a drift. I actually have experienced that in the center of Moscow on an extreme slope near the river.

Drift can happen when you go up too because of the drag but in that case the car would likely slow down by itself due to gravity.

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  • Keep in mind that most of a passenger car's braking effort comes from the brakes on the steer (front) axle -- this is especially true for cars that have discs in front and drums in back.
    – UnrecognizedFallingObject
    Dec 24, 2015 at 17:40
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    Yes, exactly, but its the same disregarding the up/down direction, that's why i did not mention this.
    – George Polevoy
    Dec 24, 2015 at 20:27
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Usually driving down a steep hill with narrow turns is more dangerous down than up for the simple reason that gravity will accelerate you going downhill.

Going up hill gravity slows you down and your engine needs to work to overcome that which usually means that you're not driving fast enough to lose control, although the condition of the road may still play a part in putting you in danger.

You can take a look at several guides relating to downhill driving for steep hills including the list below:

But if you're a visual sort of person:

While it doesn't explain everything it gives a fairly decent guide to the dangers.

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  • I don't get it, can't you just brake to avoid accelerating? I feel like the issue isn't what could go wrong with your control, but rather it's what's more likely to go wrong with the car. I think what you should have probably said is that by going uphill you can avoid overheating/damaging your brakes and in fact you can make the engine do the work instead of the brakes, which is much less likely to fail.
    – user541686
    Dec 23, 2015 at 12:19
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    @Mehrdad Brakes can and do overheat, leading to uncontrollable acceleration. Some places even have special pull offs to prevent run away trucks (as well as run away truck ramps). Sign for a pull off (sorry the image is not entirely clear; it reads "Trucks Turn out ahead Cool your brakes").
    – Randall
    Dec 23, 2015 at 15:35
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    @Mehrdad When you brake that energy goes somewhere. Unless you're driving a hybrid or electric that somewhere is heat. The brakes get hot. When they get hot enough they quit working properly. I've been a passenger in a collection of problems pretending to be a truck that had this happen--multiple miles at about 45 mph on a poor dirt road, topped off with a military checkpoint at the bottom of the hill. Fortunately they realized we were a runaway rather than trying to crash their checkpoint.
    – Loren Pechtel
    Dec 23, 2015 at 17:32
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    @Mehrdad If you have ever tried braking on a downhill in a heavy rain or on an icy or a snow covered road you would have found it equally useless since in both cases you're likely to lose traction an what happens after is anyone's guess. I've seen the results for both and it is equally not pretty. Brake overheating could be a problem but sliding sideways during aquaplaning or just on ice is a heluva lot worse.
    – Karlson
    Dec 23, 2015 at 20:13
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    @Mehrdad The answer is not as confusing as the comments you're leaving.
    – Karlson
    Dec 24, 2015 at 0:32
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Pick the side that hugs you closest to the interior.

No matter if it zig-zags or has switchbacks, take a look at it and stick to the inside. In Australia, this may mean taking the route that hugs the left side. In Oman, this always meant the route that hugged the right side.

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    Probably good advice... but it's not always clear which one does this more, especially if there are a lot of switchbacks, and if the route is long enough, you may end up with roughly a 50/50 split.
    – Flimzy
    Dec 23, 2015 at 9:05
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    +1 but one exception - in some regions where traffic is rare (e.g. rural Kyrgyzstan) it's alarmingly common for cars to take a racing line around corners, cutting into the inside lane even if that means taking a blind corner at speed on the wrong side of the road ("Dangerous? Nah, I've never met anyone who died doing this. The blackened skeletons in those burnt out wrecks we passed clearly didn't have my mad skillz"). Thankfully there aren't many places this is common... Hammering the horn while approaching blind bends is a wise tip in such places
    – user56reinstatemonica8
    Dec 23, 2015 at 20:49
  • @user568458 - Yeah, you're not just whistlin' dixie, that's a really important thing to consider. I guess any answer has to be very location specific.
    – Mikey
    Dec 23, 2015 at 20:54
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    @user568458: I experienced this as a passenger in a taxi in Jordan in 1999. I had no idea that this is common. In that particular case, on the road from Aqaba to Petra, there actually was a fair amount of traffic and bicycles in the road, no regard for human life at all! I'll tell you about the driver passing a slower vehicle on a blind turn and us coming upon a truck passing another truck coming the other way on that same blind turn. I almost left that taxi a religious man, and yes there was a skid and sudden stop involved (no collision though).
    – dotancohen
    Dec 23, 2015 at 23:21
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Ultimately the mountain road is equally safe either direction. The difference would be your driving skills, those of the other drivers on the road at the same time and the current road surface condition (wet, icy, dry).

If you are comfortable and practiced with driving mountain roads, then either direction is about the same. If you are inexperienced, then generally up hill is less stressful.

But you also have to take into consideration the terrain on both sides of the road, as going uphill on side of the road that sits a top a sheer cliff would be much more stressful than coming down the other side against the mountainside.

Your scenario of a truck careening downhill is equally dangerous to both directions, as it just just as easy take you out with a rear end collision as a head on one.

Bottom line, it depends on your driving skills.

Tom's mountain driving "rules of thumb" ... Use your transmission to control your speed, not your brakes ... Come down the steep grade in one gear lower than you went up (assuming up and down are similar grades ;-) ... Slow down before you enter the curve ...

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  • 4
    +1 for "use your transmission to control your speed" - this is a lot easier on manual shift cars. Also worth mentioning that traction is important in both directions; good wheels and appropriate tire pressure is a must.
    – Burhan Khalid
    Dec 23, 2015 at 5:34
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    You can use an automatic transmission just the same in this speed control aspect aspect ... though I do dislike these new 6 speed autos that have paddle switches. too slow to reach the gear of preference.
    – user13044
    Dec 23, 2015 at 5:59
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    But rear end collisions are usually less serious than head on collisions because the relative speed is lower.
    – orizon
    Dec 23, 2015 at 10:25
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    @orizon - Yes, a head on collision will likely kill you outright, while a rear ender will leave you conscious to enjoy the view as your car gets pushed over the edge.
    – user13044
    Dec 23, 2015 at 10:37
  • You sir, have a very different definition of the word 'enjoy'.
    – Vinayak
    Dec 24, 2015 at 16:41
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I think the relative risk depends on the road, the traffic, your skill as a driver, and other conditions.

If it's a relatively empty road (very low traffic), then going up is probably safer, as the only risk you're facing is your own inability to navigate the road, versus the downhill risk of burning out your breaks and losing control of the vehicle due to mechanical failure.

But consider the other extreme: Very heavy traffic, large vehicles, in a region where safety practices are not well enforced. In such a scenario, going uphill may be more dangerous, as the odds of being hit head-on by an out-of-control truck may outweigh the risk of losing control yourself while going down hill.

Other factors which are likely to change the equation:

  • 2-lane road or 4-lane road (or some other configuration)
  • Is it a divided highway?
  • Is the road icy? Wet?
  • Is it windy?
  • Is the road in good repair?

In summary, I expect the only truly useful way to answer this question would be to look at statistics for the particular road you're considering driving. Unfortunately, while statistics are often kept for specific segments of roads or certain intersections, I'm not aware of any agencies which track accident rates based on the traffic direction (divided highways being a likely exception to this).

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I am a terrible driver and can have mishaps at the drop of a hat. For the scenario you have described, I would consult the navigator and attempt to infer the route that has the most traffic. This route would be preferable to me because with lots of traffic one can get 'inside' a group of cars somewhere near the end. This would be my strategy if the road conditions are poor, uphill/downhill makes no difference.

Trucks and lorries that careen out of control would most likely take out those at the front of the group. And for visibility, you are better off with a string of tail lights in front of you so you can minimally stay on the road and be alerted to something when the 'group leaders' apply the brakes.

Most importantly, when something bad happens, there will be other drivers who (in Europe) are required to stop and give aid.

For you're asking for 'actual accident data', I can contribute some personal experiences. I was run off the road three times on the continent, one of them dangerously so.

The road to Mount Athos is basically flat until you reach the last city, Ouranopouli, and then it is full on treacherous. There are just narrow and twisty dirt roads with lots of 'thrilling' hairpins. In my case I was driving uphill and got run off by a lorry going downhill who was coming out of a hairpin. This was about 2AM, rainy, foggy, and all-around horrible conditions. The problem with Mount Athos is you don't get the choice of roads, the border has one drivable road leading to it and then you have to park and hike in. Drive in the day time. Optimally get behind a big lorry and follow them in/out until you're past the nature park. There's a good reason people prefer to take the ferry!

Another time on the Route Napoleon I got run off voluntarily by a group of motorcyclists who were passing me on a hairpin. Essentially I got spooked and pulled over to avoid any sort of accident caused by on coming traffic. I am an erstwhile guide on the Route Napoleon, but will never undertake it between September and May. In the summer there are lots of motorcycle clubs who converge on the route because of the 'thrills' it offers: no guard rails, mountainous roads, horrifying stone arches at the head of hairpin curves, and gorgeous scenery to die for. Again, leave Cannes early on a clear day, like 9 or 10AM and plan to arrive in Grenoble that afternoon or stop along the way well before dusk.

And another time on a twisty road outside of Bayreuth. Again this was voluntary because there wasn't enough room for me and the lorry approaching. No collision and no permanent damage, but jarring nonetheless.

See also: Britain's most dangerous roads (I will not even think about driving on these).

So to square the circle, the answer to your question which direction is safer, uphill or downhill; my answer is they are both equally safe/dangerous.

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  • +1 this is also a good strategy if you are a herbivore migrating across a savannah populated by lions. Can't argue with evolution
    – user56reinstatemonica8
    Dec 23, 2015 at 21:01
  • Interestingly your "Britain's most dangerous roads" mostly aren't so mountainous. I was expecting Hardknott and Wrynose with 25 to 30% grades, or Tan Hill in Yorkshire, or Porlock in Devon, or the single-track Assynt roads in NW Scotland. (These are fun on a bicycle, as is Izoard from your Route Napoleon!)
    – user_1818839
    Dec 24, 2015 at 11:46
  • @BrianDrummond, actually the Lake District has been the site of several blow-outs from rocks and pot holes on the road requiring the attendance of the RAC (plus having to walk to someplace with enough signal strength to call them). But there was never any oncoming or following traffic.
    – Gayot Fow
    Dec 24, 2015 at 13:12
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I always was told "What goes up must come down"

There have been valid points made for both directions.. here's my take on it for WHEN you lose control

Losing control while traveling downhill, you can release your brakes and work on regaining control Losing control while traveling uphill, you come to a stop.. at least at first, if the road is REALLY bad, you'll start sliding downhill, and you won't have a chance to even steer.

My advice? GOOD WINTER TIRES.. no all-season crap, studs are a good idea, but cable chains will get you through some pretty nasty stuff too

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  • 2
    It will be summer in Australia this weekend.
    – phoog
    Dec 25, 2015 at 7:33

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